Allow the Python binding to build without prior installation of libfko

In order to build the Python binding for Debian, I had to update setup.py to find the libfko header and libfko soname in the build env as previously done for the libfko-perl package. I cannot installed the libfko when trying to build the Python binding, this is the reason of these changes.

I have checked and I am also able to build the Python binding with libfko-dev installed on my Debian system.

I can add the changes as a patch in my Debian build, but if you think it is worth merging it to your sources, please do so.

Regards,